[Pkg-xen-devel] Bug#879751: xen-utils-common: /etc/init.d/xen restart kills running domU qemu processes

[Kojedzinszky Richárd]

Dear devs,

I still consider this issue a bug. Actually, I think the 'kill all qemu 
processes' way does not solve any issues that might arise during an 
upgrade, even it may cause more trouble. If that is a real concert, a 
preinst script might check for running qemu processes, and break if it 
founds one. I myself am not real familiar with xen internals, why is a 
dedicated qemu process needed for dom0, but for the init script it seems 
to be enough to just kill that one only, not all.

I do not understand fully the involved code, in qemu_stop_real() the 
script kills the qemu process for dom0 with a known pid in pidfile, and if 
it succeeds will kill any other qemu processes also. Is this the intent?

Regards,

Kojedzinszky Richárd
Euronet Magyarorszag Informatika Zrt.

On Mon, 18 Dec 2017, Kojedzinszky Richárd wrote:

> Date: Mon, 18 Dec 2017 08:41:06 +0100 (CET)
> From: Kojedzinszky Richárd <kojedzinszky.richard at euronetrt.hu>
> To: Hans van Kranenburg <hans at knorrie.org>
> Cc: 879751 at bugs.debian.org
> Subject: Re: xen-utils-common: /etc/init.d/xen restart kills running domU qemu
>      processes
> 
> Dear Hans,
>
> Thanks for your reply. Actually, the problem is that the script kills ALL 
> qemu processes, not only those attached to xen domU domains. I think that is 
> a problem.
>
> Would that be nice that a bash upgrade would kill all running bash processes? 
> And also, in earlier debian releases, this was not the case, I could upgrade 
> the xen-common package without any issues. Of course, a whole xen 
> (hypervisor) upgrade might need a reboot, but just a xen-common upgrade might 
> not. Right now it seems to me it breaks thing more than it helps.
>
> Regards,
> Kojedzinszky Richárd
> Euronet Magyarorszag Informatika Zrt.
>
> On Sun, 17 Dec 2017, Hans van Kranenburg wrote:
>
>> Date: Sun, 17 Dec 2017 20:08:37 +0100
>> From: Hans van Kranenburg <hans at knorrie.org>
>> To: 879751 at bugs.debian.org,
>>     Richard Kojedzinszky <kojedzinszky.richard at euronetrt.hu>
>> Subject: Re: xen-utils-common: /etc/init.d/xen restart kills running domU 
>> qemu
>>      processes
>> 
>> Hi Richard,
>> 
>> it's recommended to only actually upgrade xen packages just before you
>> want to reboot the system, and when you already stopped all domUs.
>> 
>> This is e.g. a similar situation to upgrading the openvswitch package,
>> which will also restart processes and mess up all network interfaces of
>> running domUs.
>> 
>> For unattended-updates, you can just stuff "xen" inside your
>> Unattended-Upgrade::Package-Blacklist, or if you're not using that you
>> can put all xen related packages on hold manually and only forcibly
>> include them to be upgraded just before the reboot.
>> 
>> Upgrading the xen packages while domUs are running can result in a wide
>> range of scenarios which will cause problems. Solving all of those would
>> require more work and adding far more complexity to the packages than
>> there's programmers and testers (and hardware to test all scenarios etc)
>> available in the Debian project to make that happen currently.
>> 
>> Hans
>